/Engine/Source/Runtime/GeometryFramework/Public/Components/MeshRenderDecomposition.h
FMeshRenderDecompositionrepresents a decomposition of a mesh into "chunks" of triangles, with associated materials. This is passed to the rendering components to split a mesh into multiple RenderBuffers, for more efficient updating.
class FMeshRenderDecomposition
TArray<TUnique...
Groups
TArray< int32 >
TriangleToGroupMap
Mapping from TriangleID to Groups array index.